1. Field of the Invention
The present invention relates to a variable displacement type compressor. More particularly, the present invention relates to a variable displacement type compressor used for an air conditioner incorporated in a vehicle, for example.
2. Description of the Related Art
In general, a refrigerating circuit of an air conditioner for a vehicle includes a condenser, an expansion valve, an evaporator and a compressor. The compressor sucks refrigerant gas from the evaporator, compresses it and discharges the thus compressed refrigerant gas to the condenser. In the evaporator, heat exchange is conducted between the refrigerant flowing in the refrigerating circuit and the air flowing into the passenger compartment.
In general, the compressor mounted on the vehicle is driven by the power of the engine of the vehicle, and the power of the engine is used by the compressor when the air conditioner of the vehicle is operated. Accordingly, when the vehicle is accelerated or the vehicle is driven while it is climbing a hill and when a heavy load is required for the compressor, the power of the engine becomes insufficient and the acceleration performance or the driveability of the vehicle is deteriorated. In order to solve the above problems, there is provided a variable displacement type compressor which can be driven in a small-capacity condition when the vehicle requires a higher power for running.
The variable displacement swash plate type compressor, which is commonly used as a compressor mounted on the vehicle, includes a plurality of cylinder bores, a crank chamber, a suction chamber and a discharge chamber formed in the housing of the compressor, pistons being reciprocatingly arranged in the cylinder bores. A drive shaft to which the power is transmitted from the engine (external drive source) of the vehicle is provided through the crank chamber. A rotary support body (lug plate) fixed to the drive shaft is operatively connected to the swash plate (cam plate) via a hinge mechanism (connection guide mechanism). The swash plate, converting a rotary motion of the drive shaft into a reciprocating motion of the pistons, can rotate with the drive shaft and can tilt with respect to the drive shaft while the swash plate is slid in the axial direction of the drive shaft. A stroke of the reciprocation of the pistons, that is, a displacement or a discharge capacity is determined by the inclination angle of the swash plate. However, the inclination of the swash plate is mainly determined by a difference between the pressure in the crank chamber controlled by the capacity control valve and the pressure in the cylinder bore, which act on opposite sides of the pistons.
In the variable displacement type compressor, in the case where the compressor is continuously driven under the condition that the peripheral temperature is low, there is a possibility that the evaporator is frozen. In order to prevent the occurrence of freezing, it is necessary to stop the operation of the compressor. It is a conventional technique that the power of the engine is transmitted to the drive shaft (rotary shaft) of the compressor via an electromagnetic clutch and that the compressor is driven via the electromagnetic clutch in the case of cooling and dehumidifying. However, problems are caused in the compressor having the electromagnetic clutch, because the manufacturing cost of the compressor is high and further the weight of the compressor is heavy. In order to solve the above problems, Japanese Unexamined Patent Publication No. 9-145172 discloses a vapor compression type refrigerating machine into which a variable displacement swash plate type compressor is incorporated, wherein a flow control valve for shutting off the flow of refrigerant or reducing a flow rate of refrigerant is arranged in the middle of the refrigerant passage provided between the outlet of the evaporator and the suction chamber (low pressure chamber) of the compressor.
As shown in FIG. 6 of the attached drawings, a flow control valve 70 is arranged in a valve holding hole 73 formed between a suction port 71 connected to an outlet of an evaporator (not shown) and a low pressure chamber (suction chamber) 72. The flow control valve 70 includes a valve casing 74, a valve element 75 and a compression spring 76. The valve casing 74 is arranged perpendicular to a suction passage 77 and includes an inlet port 78 for communication with the suction port 71, and an outlet port 79 for communication with the low pressure chamber 72. The valve element 75 is urged to the open side by the compression spring 76. When the pressure in the discharge chamber is supplied to the pressure chamber 80, the valve element 75 is moved to a closed position. In the middle of the passage connecting the pressure chamber 80 to a discharge chamber, there is provided an electromagnetic opening and closing valve.
In the case where it is unnecessary to cool the evaporator, for example, in winter, the electromagnetic opening and closing valve is opened, so that the valve element 75 is kept at a closed position. In this connection, there is provided a small clearance between the inner circumferential surface of the valve casing 74 and the outer circumferential surface of the valve element 75, and therefore, a small quantity of refrigerant vapor and lubricant flows through this clearance. Accordingly, the quantity of refrigerant sucked from the evaporator into the compressor becomes very small, and there is no possibility that the evaporator is frozen even if the operation of the compressor is not stopped. As a result, it is possible to omit the electromagnetic clutch.
However, in the above conventional device, when the suction passage 77 is closed, it is not completely closed but the small clearance is formed between the valve casing 74 and the valve element 75 so that a small quantity of refrigerant gas and lubricant can flow through it. However, in the case where a quantity of refrigerant gas is reduced to a value at which the evaporator is not frozen while the refrigerant gas discharged from the compressor is flowing in the circulating circuit from the external refrigerant circuit including the evaporator to the compressor, it is difficult for the lubricant, which is discharged from the compressor into the external refrigerant circuit together with the refrigerant, to return to the compressor together with the refrigerant. As a result, when the compressor is continuously operated over a long period of time in winter, the quantity of lubricant accommodated in the crank chamber becomes insufficient, and there is a possibility that the sliding sections in the crank chamber seize up and deteriorate early.
In the structure of the flow control valve 70 disclosed in the above patent publication, the valve element 75 is arranged to move between the open position and the closed position, crossing the suction passage 77. Therefore, under the condition that the valve element 75 is located at the closed position, refrigerant gas flows from the suction port 71 to the low pressure chamber 72 via the clearance formed for the valve element 75 to slide in the valve casing 74. As a result, even if the clearance is not positively provided, it is impossible to reduce the quantity of refrigerant gas returning to the compressor via the external refrigerant circuit to zero, that is, lubricant is gradually removed from the compressor. As a result, the quantity of lubricant in the compressor becomes insufficient.
The present invention is made to solve the above problems, and the object of the present invention is to provide a variable displacement type compressor, by which an evaporator in an external refrigerant circuit is not frozen even if the operation of the compressor is continuously conducted at a minimum displacement state, and it is possible to prevent the compressor from falling into an insufficiently lubricating condition.
According to the present invention, there is provided a variable displacement type compressor comprising: a housing having cylinder bores, a crank chamber, a suction chamber and a discharge chamber formed therein; a suction passage for introducing refrigerant gas from an outer refrigerant circuit into the suction chamber; a discharge passage for discharging refrigerant gas from the discharge chamber to the outer refrigerant circuit; pistons slidably arranged in the cylinder bores; a drive shaft extending through the crank chamber; a cam plate mounted on the drive shaft for rotation with the drive shaft, tiltable with respect to the drive shaft and operatively coupled to the pistons to convert the rotation of the drive shaft into the reciprocating motion of the pistons; a pressure control device for controlling the pressure in the crank chamber to change an inclination angle of the cam plate to change the displacement of the compressor; a first valve arranged in the suction passage for opening and closing the suction passage, the first valve having a valve element and a pressure chamber applying a pressure to the valve element, the first valve being arranged such that the valve element can hermetically close the suction passage when the refrigerant gas is introduced into the pressure chamber; a first passage for introducing the refrigerant gas from the discharge chamber into the pressure chamber; a second passage branched from the first passage at a branch point and leading to the crank chamber; and a control device arranged such that the refrigerant gas can be introduced from the second passage into the crank chamber when the refrigerant gas is introduced from the discharge chamber into the pressure chamber and that the flow of the refrigerant gas from the crank chamber to the first passage is blocked when the introduction of the refrigerant gas from the discharge chamber into the pressure chamber is stopped.
The compressor of the present invention is used by being connected to an external refrigerant circuit. When it is unnecessary to compress refrigerant gas, by the compressor, the compressor is operated at the minimum displacement. In the operation at the minimum displacement, the discharged refrigerant gas is supplied from the discharge chamber to the pressure chamber of the first valve, and the first valve is moved to the closing position where the suction passage is tightly or hermetically closed. Accordingly, a flow of refrigerant gas from the external refrigerant circuit to the compressor is shut off, and refrigerant gas circulates in the compressor, so that lubricant is prevented from being taken away to the external refrigerant circuit. When it is necessary to compress refrigerant by the compressor, that is, in the case of the normal operation of the compressor, the supply of the discharged refrigerant gas to the pressure chamber is stopped, and communication between the crank chamber and the pressure chamber of the first valve is shut off, so that the first valve can be opened. Then, refrigerant gas compressed by the compressor is discharged from the discharge chamber to the external refrigerant circuit and returned from the suction passage to the compressor via the external refrigerant circuit.
Preferably, the control device comprises an electromagnetic valve arranged in the first passage between the branch point and the discharge chamber and a check valve arranged in the second passage.
In this arrangement, when the electromagnetic valve provided in the first passage is opened, discharged refrigerant gas is supplied from the discharge chamber to the pressure chamber of the first valve. A portion of the discharge gas is supplied into the crank chamber via the check valve in the second passage. When the electromagnetic valve is closed, the supply of discharge gas into the pressure chamber and the crank chamber via the first and second passages is stopped. Accordingly, it is possible to simplify the structure of the control device for supplying and stopping discharge gas to the pressure chamber and the crank chamber.
Preferably, the housing has a wall having a surface and a port formed through the wall and opening at the surface, the port constituting a portion of the suction passage, the valve element of the first valve being arranged to face the surface and movable in the direction perpendicular to the surface, the pressure chamber being arranged on the side of the valve element remote from the surface of the wall.
In this arrangement, the valve element closes the suction passage under the condition that the valve element comes into contact with the surface of the wall which forms the suction passage. Clearance necessary for the valve element to be moved is independent of a portion of the valve where the suction passage is closed. Accordingly, the suction passage can be tightly closed by a simple structure.
In this case, preferably, the first valve includes a valve housing in which the valve element is slidably arranged, the valve element having a front end extending from the valve housing and abutting against the surface of the wall when the first valve is in the closed position, the valve element having a back end arranged in the valve housing, the pressure chamber being formed by the back end of the valve element and the valve housing.
Preferably, the first valve includes a spring urging the valve element in the valve open direction.
In this arrangement, when the supply of discharge gas to the pressure chamber is stopped, the valve can be opened by the action of the spring. As a result, no suction pressure loss is caused when the compressor is operated in the case of turning on the air conditioner.
Preferably, the first valve includes a spring urging the valve element in the valve close direction.
In this arrangement, even if the displacement (minimum displacement) in the case of turning off the compressor is reduced, it is possible to hold the valve element at a position where the suction passage is tightly closed.